Plugin class to calculate Bemis-Murcko and other structural scaffolds of input
molecules.
The plugin inside executes a series of atomic (not in chemical sense) operations
which are accessible to the user. The configuration which is set either by
setParameters( Properties ) or by the individual setters. The operation
chain is set up according to the actual configuration by getHost( boolean ).

checkMolecule

Checks the input molecule.
Throws exception if the molecule is not accepted as input molecule,
otherwise does nothing (simply returns).
In addition to the default implementation (which refuses query molecules,
molecules with SRU S-groups, molecules with multicenter S-groups and
molecules with coordinate bonds) this method will check if Frameworks
can be executed on the structure.

Currently the following cases (in addition to the default behavior)
fail:

mcs Framework calculation needs at least two disconnected
fragments. If the molecule contains no atoms or consists of one connected
fragment exception is thrown.